DESCRIPTION: (Applicant's Description) The animal core provides the following services related to preparation and characterization of animal models to study DNA repair: (1) Preparation of new transgenic mouse lines. The core is responsible for final purification and pronuclear injection of DNA constructs provided by P01 members, transfer of injected embryos to oviducts of foster females, and identification of transgenic founder mice by PCR and Southern blotting. (2) Preparation of mice with endogenous genes modified by homologous recombination. Investigators provide the core with DNA targeting constructs. The core prepares embryonic stem cell lines carrying the altered gene, transfers these cells to blastocysts, transplants blastocysts to the uterus of foster females, identifies chimeric mice by coat color, and confirms genotype by PCR and/or Southern blotting. (3) Mouse embryo cryopreservation. This service is critical to reduce costs of animal maintenance and to protect investigators from catastrophic losses of animal lines caused by disease, accidents and any other causes. The core collects, freezes, stores and recovers mouse embryos. (4) Preparation and archiving of animal cells and tissues. This service assures consistency in quality of experimental materials shared by investigators, reduces the number of animals, and eliminates duplication of time-, cost-, and labor-consuming animal experiments. The core assists investigators in the collection of mouse tissues, setting up primary cell cultures, and processing tissue specimens for the preparation of frozen or paraffin sections. The core will stain sections with hematoxylin and eosin, and will perform laser capture microdissection for DNA and RNA analyses. (5) Consulting services. The core staff will provide advice on the design of transgene constructs, handling of embryonic stem cells, maintenance of animal colonies, designing chemical and irradiation carcinogenesis protocols, and tumorigenicity tests in vivo. The core will also advise on specific pathological techniques, such as immunostaining, in situ hybridization and TUNEL analyses. (6) Development of new animal models to study DNA repair and tumor suppressor genes. The core is developing animal models with conditional regulation of gene function. Targeted Cre-lox recombination and tetracycline-mediated regulation, either singly or in combination, are currently being used.